Why last week’s solar storm was a dud

When the largest flare in four years erupted from the sun February 14,
sky watchers across the Northern Hemisphere braced themselves for a
geomagnetic storm. Space weather experts predicted that jets of
charged particles smacking into the Earth's magnetic field could
disrupt navigation and communication systems, and spark a bonus of bright northern lights dancing across the
ionosphere.

Instead, nothing much happened.

"There were some nice displays of aurora, but you had to live in
Finland, northern Canada or Alaska to see them," said Joe Kunches,
a forecaster at the National Oceanic and Atmospheric
Administration's Space Weather Prediction Center. "This one was
the lowest storm category that we even pay any attention to."

The storm was so weak because the flare's magnetic field
happened to be aligned parallel to the Earth's. When the sun sends
a mass of hot plasma hurtling toward the planet in a coronal mass ejection, the plasma is imprinted
with its own magnetic field separate from the sun's. Astronomers
can't predict the direction of the plasma's magnetic field until
the burst hits Earth.

If the plasma's magnetic field is parallel to the Earth's, the
incoming charged particles are effectively blocked from entering
Earth's magnetosphere. An identical flare with a perpendicular
magnetic field would have triggered a much stronger storm.

"If the magnetic fields are parallel, then the shields are up.
We are well protected," said space weather expert Juha-Pekka
Luntama of the European Space Agency February 19 at the meeting of
the American Association for the Advancement of
Science in Washington, DC.

But next time we might not be as lucky with alignment, and we
can expect up to 1,700 more storms like last week's in the coming
months as the sun wakes back up.

NOAA ranks geomagnetic storms on a scale from G1, minor storms that spark auroras
in Michigan and Maine, to G5, extreme storms that can shut down power grids and cause
northern lights as far south as Florida. The ranking is based on
how much more active the local magnetic field is than a normal,
quiet day.

The February 14 storm turned out to be a G1, meaning "it wasn't
that big a deal," Kunches said.

The storm was mostly notable for being the first of the new
solar cycle, Kunches said. The sun goes through periods of relative
violence and calm every 11 years or so. This last solar minimum was
longer and quieter than astronomers expected. Many predict that the
ensuing solar maximum, when magnetic activity on the sun will cause
more frequent and severe flares, will also be relatively
serene.

But space-weather experts are more nervous about this solar
maximum than ever before. Since the last solar maximum in 2000,
society has grown more dependent on systems that can be knocked out
by a strong solar flare.

A strong flare would send ultraviolet and X-ray radiation to the
sunlit side of the Earth, ionizing the upper atmosphere and
potentially shutting down GPS satellites. Losing GPS would cause
chaos in more than just car navigation systems, Bogdan said.

"GPS is involved in everything we do," he said, including
financial transactions. Prices fluctuate so quickly that traders
need a time stamp accurate to a millionth of a second every time
they buy or sell something. Every time you swipe your credit card
at the gas station or buy a bag of oranges, Bogdan said, it goes
through a GPS satellite.

Ten to 20 minutes after the flare, a burst of high-energy
protons would enter the Earth's magnetic field at the poles,
causing processing errors in other satellites.

About half an hour later, the hot cloud of plasma that the sun
spit out with the flare would bump into the Earth's magnetic field.
If it's strong enough, the plasma's magnetic field can induce
currents in electric transmission lines, which could cause
widespread blackouts. The most powerful solar flare in recorded
history, the Carrington flare in September 1859, sent
currents through telegraph wires and even set a few buildings on
fire.

Bogdan noted that that storm and the next-strongest storm in
1921 both happened during particularly weak solar cycles.

Still, he said, "don't panic." Many satellites and transmission
lines are already fitted with shields to prevent the worst of the
damage from a strong flare. Others can be shut down preemptively.
Sun-observing satellites give space weather experts about 20 hours
to come up with a plan to deal with an impending storm, during
which NOAA sends out detailed alerts.

"This recent solar flare really illustrates that we need to pay
attention to space weather," said NOAA administrator Jane
Lubchenco at the AAAS meeting. "The watchword is, predict and
prepare."

Interested sky watchers can sign up to receive space-weather alerts on
their phones, and watch for more flares in the next two years. NOAA
predicts 100 storms that will spark auroras as far south as
Alabama.